The invention relates to the field of fluid catalytic cracking of hydrocarbons, especially heavy hydrocarbons, containing contaminant metals and, more particularly, to a compound for passivating such contaminant metals.
Fluid catalytic cracking is a frequently used process for cracking heavy hydrocarbon feedstocks into lighter, more useful fractions and especially into gasoline.
Catalysts used for such processes are of numerous types and include zeolite type catalysts of both natural and synthetic origin. Zeolite catalysts are characterized by crystalline aluminosilicate structure which serves as a molecular sieve and active compound to yield the desired cracking activity and products. The effectiveness of the zeolite catalyst is greatly diminished, however, when certain contaminant metals are present in the feedstock. Of particular significance as contaminant are nickel, vanadium, iron, copper and chromium. These metals are deposited upon the catalyst during cracking and significantly interfere with the function of the catalyst to obtain desired cracking products.
Passivation is a procedure which is used to reduce the adverse effects of contaminant metals in the feedstock. This technique involves the introduction of reactants into the feedstock or catalyst which interact with the contaminant metal and render same inert so as to protect the catalyst from the harmful effects of such contaminants.
Antimony and tin are known passivating agents and are useful for passivating nickel and vanadium respectively.
U.S. Pat. No. 4,321,129 to Bertus et al deals with the use of antimony and tin to regenerate activity in used catalysts. Bertus et al. teach the treating of such a used FCC catalyst individually with antimony compounds and then with tin compounds so as to passivate contaminant metals. The catalyst is impregnated with each compound separately. Further, Bertus et al. teach the use of antimony compounds and tin compounds which include other contaminants such as sulfur and phosphorus.
U.S. Pat. No. 4,466,884 to Occelli et al. also teaches the use of antimony and tin to passivate contaminant metals. As with Bertus et al., antimony and tin are used in separate compounds that each include additional contaminants such as sulphur and phosphorus. Further, Occelli et al. report the use of titanium, aluminum and calcium oxide containing compounds as diluents for the tin and antimony. However, titanium, aluminum and calcium oxides are reported to be passivating agents. See for example U.S. Pat. Nos. 4,816,135, 4,704,375, and 4,432,890. Thus the improved results of Occelli et al. are no doubt at least partially due to the use of additional passivating agents.
It is a principal object of the present invention to provide a single compound containing both antimony and tin which compound can be added to a feedstock or can be impregnated into a catalyst to passivate contaminant metals in the feedstock.
It is another object of the present invention to provide a process for preparing an antimony and tin containing compound in accordance with the invention.
It is a further object of the invention to provide such a process and compound wherein the compound is essentially free of sulfur, phosphorous, and other undesirable contaminants.
It is still another object of the present invention to provide a process whereby an antimony and tin containing compound is used to passivate contaminant metals in a feedstock for a fluid catalytic cracking process.
Further objects and advantages of the present invention will appear hereinbelow.